When you have found your perfect student house or flat to share, in most cases you will be expected to nominate a guarantor - someone who will take over the rent payments if you default on the rent.
If you are renting with other students and have one tenancy agreement, there will usually be one guarantor to cover the whole rent. Once a suitable person is nominated (usually a parent), they will also need to sign paperwork and often show ID, so make sure they are fully aware of what they are entering into.
You will need to pay something to secure your property so that no one else can come in and take it after you have decided it's the one for you. The most common form of payment is a deposit which as well as securing the property is also an assurance for the property's owner that any damage to the property will be covered by this cost as well. An average cost would be around £250 per student and this is protected under the TDS (Tenancy Deposit Scheme). You will have this returned at the end of the tenancy as long as there has been no defaults in payment or damage to the property.
Some lettings agents impose a reservation fee which is sometimes in addition to a deposit - if this is the case, it is worth you asking exactly what this covers and if it is returned at any point. If it is not worded as a deposit, it will not be covered by the TDS so any rules surrounding this will be at the agents discretion.
In a shared house, most tenancies tend to be for the whole property and therefore if someone drops out, you will need to replace them or otherwise cover the remaining rent amongst the remaining tenants.
Even if you are sharing with friends, managed accommodation/private halls will have individual tenancy agreements so if someone moves out, you will not be liable to cover their rent.
However, if you are the one leaving before the tenancy agreement expires, you will usually be expected to find someone to replace you to cover your rent as this will be in breach of your contract.
Students should make sure they check with a landlord or agent what type of tenancy agreement they are entering into before signing anything.